A number of known control arrangements regulate the position or elevation of implements, such as plows, attached to or drawn by agricultural vehicles. Such control systems generally sense the position of a three-point hitch and compare this position to a command or desired position set by an operator. The control system compares the sensed implement position to the command position and generates a control signal to an actuator to vertically move the hitch, along with the implement mounted on it, to the desired elevation.
Control systems can also operate based on draft force. For example, the control system disclosed in U.S. Pat. No. 5,421,416, filed Sep. 8, 1993, commonly assigned with the present invention and incorporated herein by reference, controls the position of a ground penetrating implement based at least in part on the draft force encountered when the implement interacts with the ground.
Agricultural vehicles equipped with known control systems can experience oscillations when the vehicle travels at high speeds across roads or between fields. The vehicle operator commands the implement to a lifted position during travel. At high speeds, the implement can oscillate or bounce due to, for example, bumps or depressions in the road or the field. The interaction of an oscillating implement with the vehicle can cause an uncomfortable ride for the operator and can cause the vehicle's front wheels to leave the road or field surface. Severe oscillations can create an undesirable condition in which the implement may approach the road or the field during transport. To compensate for the phenomena of implement oscillations, the operator may reduce the vehicle's intended travel speed. The reduced travel speed lowers the operator's productivity.
U.S. Pat. No. 4,924,943, filed Mar. 24, 1989, discloses a control system for an agricultural vehicle which provides for active damping of implement vibrations which occur when the vehicle travels around a curve with the implement raised. When the vehicle travels around a curve, part of the implement weight normally resting on the draft load force pins is shifted by side guiding members onto the housing of the tractor. This causes the force sensed by the draft load force pins to decrease. At the end of the curve, the sensed force increases as the implement weight is shifted back onto the draft load force pins. The disclosed control system uses active damping based upon a dynamic force signal to reduce the disturbing influence of the side guiding members during turning.